1. Technical Field
The present invention relates to a process for stably producing methionine over a long period of time in case of hydrolyzing 5-(β-methylmercaptoethyl)hydantoin in the presence of potassium carbonate, the process enabling excellent corrosion resistance of an equipment.
2. Description of the Related Art
A process for hydrolyzing 5-(β-methylmercaptoethyl)hydantoin (hereinafter referred to as M-hydantoin) to obtain methionine is usually carried out in such a manner as shown in the following scheme in the presence of an alkali.

This hydrolysis reaction is usually carried out under the condition of a pressure of about 0.5 to 1.5 MPaG and a temperature of about 150 to 200° C. When potassium carbonate is used as the alkali, a metallic material is extremely likely to be corroded under the hydrolysis condition regardless of a liquid phase or a vapor phase. A SUS 304L stainless steel is corroded and a high-grade austenitic chromium-nickel stainless steel, which is said to be more excellent in corrosion resistance, is also insufficient in corrosion resistance to such an environment.
Under such an environment, zirconium, which forms a stable zirconium oxide film on the surface, shows excellent corrosion resistance, but has such a problem that it is expensive and is inferior in workability.
Under these circumstances, it is known that a stainless steel containing 21.0 to 30.0% by weight of a Cr element, 4.5 to 11.0% by weight of a Ni element, 2.5 to 5.0% by weight of a Mo element and 0.05 to 0.35% by weight of a N element as chemical components in metal has excellent corrosion resistance for an equipment material in such an environment (Japanese Unexamined Patent Publication (Kokai) No. 11-217370).